Magnetic disk drive

ABSTRACT

A magnetic disk drive having a small decrease in lubricant film thickness on the surface of the magnetic disk and a superior sliding reliability between the magnetic head and the magnetic disk surface is supplied.  
     Perfluoropolyether is supplied onto the surface of the magnetic disk using heat and air flow by applying perfluoropolyether onto the surface of a suspension, or impregnating Perfluoropolyether into a filter.  
     Perfluoropolyether contains a component having a molecular weight smaller than 4000 by at least 40 %.  
     Perfluoropolyether is dropped onto a plane facing to the magnetic disk of the suspension.  
     The filter is impregnated with a specified perfluoropolyether, and the amount of impregnated perfluoropolyether is at least 0.15 μ-liter.  
     Then, a magnetic disk drive having a superior reliability can be obtained.  
     A magnetic disk drive having a small decrease in lubricant film thickness on the surface of the magnetic disk and a superior sliding reliability between the magnetic head and the magnetic disk surface can be obtained.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a magnetic disk drive.

[0002] Thickness of a lubricant film applied onto a surface of magneticdisk is decreased on account of a centrifugal force and a shear forcegenerated by rotation of the magnetic disk, and splashing by temperaturerise in the magnetic disk drive. In order to maintain sliding durabilitybetween a magnetic disk and a magnetic head slider, a lubricant issupplied onto surface of the disk, or the lubricant is applied onto thesurface of the disk. Various methods for supplying lubricants onto thesurface of disk in a magnetic disk drive are disclosed in JP-A-59-218668(1984), JP-A-60-239921 (1985), JP-A-8-45238 (1996), JP-A-10-312660(1998), JP-A-8-45239 (1996), JP-A-6-295579 (1994), Japanese Patent No.2796852, and others.

[0003] In accordance with JP-A-59-218668 (1984), a lubricant is suppliedonto the surface of magnetic disk from a venting hole at the center ofthe hub by generating the lubricant vapor from the lubricant impregnatedmember provided at the bottom of the device by heated air flow generatedwith rotation of the magnetic disk. In accordance with JP-A-60-239921(1985), a lubricant film is formed on the surface of magnetic disk bydepositing from myristic acid vapor, which is vaporized from a myristicacid impregnated member by blowing hot air thereon,. In accordance withJP-A-8-45238 (1996), a lubricant film made of a liquid lubricant isformed on an arm or a suspension, and the lubricant is supplied onto thesurface of magnetic disk by an air flow accompanied with rotation of themagnetic disk. In accordance with JP-A-10-312660 (1998), JP-A-8-45239(1996), and Japanese Patent No. 27906852, a liquid lubricant is suppliedonto the surface of magnetic disk by placing a wick material, whereinthe liquid lubricant having a low viscosity is impregnated, in thevicinity of the disk. In accordance with JP-A-6-295579 (1994), alubricant is supplied from a reservoir provided with a heating element.

[0004] Thickness of lubricant film on the disk maintains a definitevalue under a condition that an amount of the lubricant reduced byscraping-off and splashing is balanced with an amount of the lubricantsupplied by heat and air flow, and sliding durability between themagnetic disk and the magnetic head slider is ensured. However, if thebalance is lost, the lubricating performance is lowered by continuousdecrease of the lubricant film thickness, or reversely, too muchincrease of the lubricant film thickness. Furthermore, another cause fordecreasing the sliding performance is contamination of the head sliderwith various contaminants which are brought into the device from bothexterior and interior of the device.

[0005] In order to solve the problem mentioned above, by supplying alubricant, physical properties of the lubricant such as molecularstructure and molecular weight, and the amount of the lubricant held inthe magnetic disk drive must be studied in detail before practical useof the lubricant. In accordance with the prior art mentioned above,optimization of supplying amount of the lubricant, physical propertiesof the lubricant such as molecular structure and molecular weight, andthe amount of the lubricant held in the magnetic disk drive are notpractically studied nor disclosed. Accordingly, stable supply of thelubricant by heat or air flow is impossible.

[0006] Furthermore, operation systems and structures of the magneticdisk drive must be considered. For instance, in accordance with a CSS(Contact Start Stop) system disclosed in JP-A-59-218668 (1984), a strongadsorption (stiction)is generated between the head slider and themagnetic disk, if the lubricant film thickness is increased, and atrouble such as difficulty in starting up of the magnetic disk and thelike are generated. Therefore, a L/UL (Load/Unload) system can be deemedas desirable for supplying a lubricant.

SUMMARY OF THE INVENTION

[0007] One of the objects of the present invention is to provide amagnetic disk drive having a small decrease in thickness of lubricantfilm on the magnetic disk surface, and a superior reliability in slidingperformance between the magnetic head and the magnetic disk surface.

[0008] In order to decrease reduction of lubricant film thickness on themagnetic disk surface, the inventors of the present invention found anoptimum molecular weight and molecular structures of lubricants whichare supplied from a lubricant holding member to the magnetic disksurface utilizing heat in the magnetic disk drive and an air flow causedby rotation of the magnetic disk. Furthermore, the lubricant holdingmembers were studied and optimized.

[0009] When the lubricant is supplied utilizing heat and/or air flow,the amount of supplied lubricant varies significantly depending on thematerial which holds the lubricant, and direction, strength,temperature, and the like of air flow at the installed location of thelubricant holding member. Necessary amount of the lubricant variesdepending on the volume of the magnetic disk drive, a number of rotationof the disk, and the number of magnetic disks mounted on the magneticdisk drive. In order to optimize the supplying amount of the lubricant,the molecular weight and the molecular structure of the lubricant mustbe specified, because physical properties of the lubricant variesdepending on the molecular weight and the molecular structure.

[0010] Perfluoropolyether, one of the lubricants for the magnetic disk,is less volatile in comparison with hydrocarbon group lubricants such asmineral oil and the like which are used for general industrial machines.In accordance with increasing molecular weight, the lubricant becomesless volatile. Accordingly, in order to supply perfluoropolyether tosurface of the disk by heat and air flow, readily volatile relativelylow molecular weight components are necessary.

[0011] Furthermore, the structure of terminal group of the lubricantmust be specified in order to optimize the supplying amount of thelubricant, because an adsorbing force of the lubricant holding memberand mutual interactions between the lubricant molecules themselves varysignificantly depending on the structure of the terminal group ofperfluoropolyether molecules. The adsorbing force between the lubricantholding member and the lubricant influences on readiness of supplyingthe lubricant, and the mutual interactions between the lubricantmolecules themselves influence on recovery of the lubricant film onsurface of the magnetic disk.

[0012] Lubricants, which can reduces as possible to adhere gases broughtinto the magnetic disk drive, gases, wear particle, and dusts generatedin the device onto sliding portions of the slider and head elementportions, are desirably selected.

[0013] Feature of the present invention is that: a lubricant supplyingmeans for supplying a lubricant to surface of the magnetic disk from aportion other than the surface of the disk is provided in the magneticdisk drive; the lubricant supplied by the lubricant supplying meansincludes at least one of the components expressed by the structuralformulas 1-5; and the component is perfluoropolyether having a molecularweight equals to or smaller than 4000. Furthermore, desirably, thecomponents having a molecular weight of at least 1000 and equals to orsmaller than 4000 are contained at least 40%.

[0014] The lubricant supplying means can be a suspension or an armapplied with the lubricant.

[0015] The lubricant supplying means can be a lubricant holding meanswhich holds the lubricant. In this case, the lubricant desirablycontains perfluoropolyether having a structure expressed by any one ofthe structural formulas 1-5. The lubricant holding means is desirablymade of a material, which can hold the lubricant without separating asthe lubricant drops, such as filter, wick materials, and the like.

[0016] The lubricant holding means is desirably a filter impregnatedwith perfluoropolyether having a structure expressed by any one of thestructural formulas 1-5. In this case, at least 0.15 μl ofperfluoropolyether having a structure expressed by any one of thestructural formulas 1-5 is impregnated, in order to reduce the amount ofcontaminant adhered to a levitated plane of the magnetic head slider.

[0017] In order to reduce the amount of contaminant adhered to thelevitated plane of the magnetic head slider and, further, to reducedecrease of the lubricant film thickness, at least 0.5 μ-liter ofperfluoropolyether having a structure expressed by any one of thestructural formulas 1-5 is desirably impregnated. The amount of thelubricant impregnated into the filter does not have any particularlimitation as far as the lubricant does not cause any trouble inoperation of the device such as generating lubricant drops and the like,and the amount of the lubricant is decided in consideration of therecovery effect of the lubricant film.

[0018] If the lubricant film formed on the magnetic disk contains atleast one of perfluoropolyether having structures expressed by thestructural formulas 1-5, the lubricant supplied from the lubricantsupplying means is readily adhered onto the lubricant film formed on themagnetic disk surface, and a high recovery effect of the lubricant filmis realized.

[0019] As for an operation system of the magnetic disk drive comprisinga lubricant supplying means, the conventional CSS (Contact Start Stop)system has an effect to prevent head crash and others. However, the L/ULsystem; in which the magnetic head slider is positioned above themagnetic disk plane only when the magnetic disk is rotating, and themagnetic head slider is escaped to an outer region from the outerperipheral plane of the magnetic disk when the rotation of the magneticdisk is stopped; is advantageous because any problems such as adsorption(stiction) and the like will not be generated.

[0020] As explained above, sliding durability between the magnetic diskand the magnetic head slider can be ensured by supplying the lubricantfrom a lubricant supplying means. Furthermore, the lubricant can besupplied stably, and any significant design change of the device andincrease in number of the components are unnecessary.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] These and other objects, features and advantages of the presentinvention will be understood more clearly from the following detaileddescription with reference to the accompanying drawings, wherein,

[0022]FIG. 1 is a schematic plan view and a schematic side view of thetesting apparatus used in the embodiment 1,

[0023]FIG. 2 is graph indicating a result of fractionation ofperfluoropolyether into eight regions depending on their molecularweights,

[0024]FIG. 3 is a graph indicating variation in lubricant film thicknessversus time in the random seek test in the embodiment 1,

[0025]FIG. 4 is a graph indicating an experimental result evaluating arelationship between molecular weight of the lubricant versus slidingperformance tested in the embodiment 1,

[0026]FIG. 5 is a graph indicating variation in lubricant film thicknessversus time in the random seek test in the embodiment 2,

[0027]FIG. 6 is a graph indicating a relationship between molecularstructures of the lubricant and supplying amounts of the lubricant inthe embodiment 3,

[0028]FIG. 7 is a schematic plan view and a schematic side view of themagnetic disk drive 14 used in the embodiment 4,

[0029]FIG. 8 is a graph indicating variation in lubricant film thicknessversus device operable time in the embodiment 4,

[0030]FIG. 9 is photographs taken from the levitated planes of themagnetic head slider 2 after 1000 hours in the device evaluation test(FIG. 8) in the embodiment 4,

[0031]FIG. 10 is a graph indicating variation in lubricant filmthickness versus device operation time in the embodiment 5, and thecomparative examples 4 and 5,

[0032]FIG. 11 is a graph indicating variation in lubricant filmthickness versus device operation time in the embodiment 6, and thecomparative example 6,

[0033]FIG. 12 is a graph indicating variation in lubricant filmthickness versus device operation time in the embodiment 7, and thecomparative examples 7 and 8,

[0034]FIG. 13 is a schematic plan view and a schematic side view of themagnetic disk drive 17 used in the embodiment 8,

[0035]FIG. 14 is a graph indicating variation in lubricant filmthickness versus device operation time in the embodiment 8, and thecomparative example 9,

[0036]FIG. 15 is a graph indicating variation in lubricant filmthickness versus device operation time in the embodiment 9, and thecomparative example 3, and

[0037]FIG. 16 is photographs taken from the levitated planes of themagnetic head slider 2 after 1000 hours in the device evaluation test(FIG. 15) in the embodiment 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] (1) A Supply Source of the Lubricant

[0039] In order to supply the lubricant by heat in the magnetic diskdrive and air flow generated by rotation of the disk in the presentinvention, a supply source of the lubricant was provided in the magneticdisk drive as follows:

[0040] {circle over (1)} The lubricant is applied onto surface of asuspension, and/or an arm. Or

[0041] {circle over (2)} The lubricant is impregnated in a lubricantholding means (filter, wick material, and the like), and the lubricantholding means is provided in the magnetic disk drive.

[0042] When the disk is rotated and the temperature in the disk deviceis rised, the lubricant is evaporated from the supply source andsupplied to surface of the disk. The filter impregnated with thelubricant was arranged so that the air flow in the device could beutilized effectively.

[0043] (2) Composition of the Lubricant

[0044] In accordance with the present invention, perfluoropolyether isused as the lubricant for supply. In order to achieve a stable supplyand a sufficient recovery function against scraped-off by the head,perfluoropolyether having an adsorptive polar group is used. And, themolecular weight of the perfluoropolyether is specified as a valuesufficient for evaporation by the temperature and supply by the air flowin the magnetic disk drive. Practically, perfluoropolyether are asfollows:

[0045] These lubricants have polar groups at both terminal ends ofperfluoropolyether chain, and a high recovery effect for the lubricantfilm, because these lubricant are readily adsorbed onto surface of thedisk. The amount of the lubricant to be applied or impregnated wasadjusted corresponding to the structure and volume of the casing of themagnetic disk drive.

[0046] (3) Composition of the Magnetic Disk of the Present Invention

[0047] The magnetic disk is composed of a substrate, whereon a seedlayer, a magnetic layer, a overcoat mainly made of carbon, and alubricant layer made of perfluoropolyether as the outermost layer areformed sequentially. The lubricant film is composed ofperfluoropolyether. Practically, the lubricant having at least astructure expressed by any one of the structural formulas 1-4 can beindicated as an example, but the present invention is not restricted tothis example.

[0048] (4) Use of the Magnetic Disk Drive of the Present Invention

[0049] The magnetic disk drive of the present invention can be used asexterior memories (practically hard disk devices and the like) inelectronic computers, word processors, and the like. Furthermore, themagnetic disk drive can be applied to mobile computers, navigationsystems, games, and various information devices such as portabletelephones, PHS, and the like.

[0050] Hereinafter, the present invention is explained in detailreferring to the embodiments.

[0051] (Embodiment 1)

[0052] An effect of supplying the lubricant was verified in the presentembodiment by measuring variation in lubricant film thickness of a casewhen a lubricant supplying source was provided on the suspension 15 andin a case when such a lubricant supplying source was not provided.

[0053] The testing apparatus 1 used in the present embodiment 1 isindicated in FIG. 1. The testing apparatus is composed based on apractical magnetic disk drive, and an evaluation under an operationalcondition as same as a practical device is possible. The magnetic headslider 2 is provided at the tip of the 'suspension 15, and thesuspension 15 is supported by the arm 3. A distortion gauge is providedinside the arm portion 3, and a friction force between head and disk canbe measured. The spindle portion and the voice coil motor portion areimproved so that the disk rotation number and the seek frequency aremade variable. In order to control the temperature inside the apparatus,a cord heater 6 is attached to the cover 5 of the apparatus, and thetemperature is made variable from room temperature to 80° C. The barheater 7 and the filter 8, which make it possible to hold the lubricantand heat it, are provided inside the apparatus. The inner volume of theapparatus is 450 ml. The magnetic disk 4 is made by forming a seed layermade of a Cr alloy, a magnetic layer made of CoCrTaPt, and a carbonovercoat, sequentially, on a glass substrate of 63.5 mm (2.5 inches) indiameter. Hardness of the carbon overcoat is enhanced by forming thefilm in an atmosphere of Ar/N₂ gas mixture, and the film thickness is 5nm.

[0054] A magnetic disk 4 was prepared by forming a lubricant film of 2nm thick made of perfluoropolyether (number average molecular weight3000) having a structure expressed by the structure formula 1 on acarbon overcoat. The film thickness was measured by FT-IR.

[0055] Perfluoropolyether having a structure expressed by the structureformula 1 was molecular weight fractionated by HPLC (High PressureLiquid Chromatography). Samples No 1 to No. 5 were prepared with themolecular weight-fractionated perfluoropolyether.

[0056] Sample No. 1: Molecular weight 1340

[0057] Sample No. 2: Molecular weight 2180

[0058] Sample No. 3: Molecular weight 3060

[0059] Sample No. 4: Molecular weight 4640

[0060] Sample No. 5: Molecular weight 7100

[0061] Each of these perfluoropolyether was dropped by 1.0 μ-liter ontothe suspension 15 plane facing to the magnetic disk 4 at a spot 16,which is 10 mm away from the magnetic head slider 2, and then, thesuspension 15 was attached to the testing apparatus 1.

[0062] A plane having a radius in the range of 16 mm to 28 mm of themagnetic disk 4 was moved to random seek (a random seek test) under anenvironment of 65° C. Rotation number of the magnetic disk 4 is 5400rpm. In accordance with the test in the present embodiment, the magnetichead slider 2 was slid on the magnetic disk 4 in a condition that itnearly comes to contact, and the magnetic head slider 2 was given a loadof 37.5 mN, which was about 1.5 times of the ordinary load (25 mN) inorder to make the test under an accelerated condition.

[0063]FIG. 3 indicates variation in lubricant film thickness on themagnetic disk 4 surface versus testing time. A case whenperfluoropolyether was not dropped onto the suspension is indicated ascomparative example 1.

[0064] The lubricant film thickness of the comparative example 1 wasdecreased to 0.3 nm after 120 hours of run. By contrast, whenperfluoropolyether was dropped onto the suspension as the sample 1-5,the lubricant film thickness was decreased very slightly. Furthermore,this result indicates a tendency that the decrease of the lubricant filmthickness becomes smaller as the molecular weight becomes smaller.

[0065] In accordance with the result on the comparative example 1, thelubricant film thickness was decreased with 0.3 nm/24 h in average whenthe lubricant was not supplied from outside the disk surface. Inaccordance with the result shown in FIG. 3, lubricant supplying rates inthe embodiment 1 can be calculated as 0.34 nm/24 h when the molecularweight is 1340, 0.3 nm/24 h when the molecular weight is 2180, 0.26nm/24 h when the molecular weight is 3060, 0.19 nm/24 h when themolecular weight is 4640, and 0.08 nm/24 h when the molecular weight7100. In order to ensure the reliability of the device by maintaining asufficient film thickness, the lubricant supplying rate must bemaintained at least 0.2 nm/24 h. As explained above, decrease of thelubricant film thickness at the surface of the magnetic disk 4 can bereduced significantly by using perfluoropolyether having a molecularweight smaller than approximately 4000 as lubricant, because even if thelubricant is scraped off from the surface of the magnetic disk 4 by themagnetic head slider 2, the lubricant is supplied from the suspension 15by heat and air flow.

[0066] In order to make a relationship between the molecular weight ofthe lubricant and the supplying rate clear, the lubricant fractionatedin molecular weight by HPLC was used in the embodiment 1. However, inpractical use in the device, use of commercial available lubricant isadvantageous in cost. In accordance with the result on the comparativeexample 1, it was revealed that the lubricant film thickness wasdecreased by a rate of 0.3 nm/24 h in average when the lubricant was notsupplied from outside. Therefore, it can be calculated from thesupplying amount of the lubricant that even if the commercial availablelubricant has a number average molecular weight larger than 4000, thedecrease of the lubricant film thickness can be reduced if the lubricantcontains a component having a number average molecular weight smallerthan 4000 by at least 40% to total weight.

[0067] As explained above, if perfluoropolyether containing componentshaving a molecular weight smaller than 4000 by at least 40% to totalweight is used, the decrease of the lubricant film thickness can bereduced by stable supply of the lubricant onto the surface of themagnetic disk by heat and air flow.

[0068] Next, a sliding durability was evaluated by sliding the magneticdisks 4, which were prepared by applying each of the samples 1-5obtained previously by molecular weight fractionation by HPLC, on themagnetic head slider 2 under a complete contacting condition. The testwas performed by sliding the magnetic disk 2 onto the magnetic headslider 2 continuously with complete contact in a condition of 150 rpmand load 11.76 mN, and the sliding durability was determined by thenumber of sliding until a disk crash occurred. The test was performed by100,000 sliding at maximum, and put a target of the sliding durabilityfor practical magnetic disk drive at least 50,000 sliding. The result ofsliding durability test is indicated in FIG. 4. Here, the result wasstudied in comparison with the sample 15, which was prepared by applyingperfluoropolyether having a molecular weight of 850 obtained bymolecular weight fractionation of the same perfluoropolyether as the oneused in the embodiment 1 by HPLC onto the magnetic disk 4 (sample 15).The sample 15 was disk-crashed at 7000 sliding, but all the othersamples of the embodiment 1 indicated a sliding durability of more than50000 sliding. From this observation, it can be concluded that thelubricant (perfluoropolyether) to be supplied desirably has a molecularweight of at least 1000, in order to endure the sufficient slidingdurability. However, it must be retained that, even if the molecularweight is smaller than 1000, an advantageous effect to prevent decreaseof the lubricant film thickness is not entirely denied as far as theresult shown in FIG. 3 is considered.

[0069] In accordance with the result explained above, decrease of thelubricant film thickness can be reduced by stable supply of thelubricant to the surface of the magnetic disk by heat and air flow, ifperfluoropolyether containing components having a molecular weightsmaller than 4000 by at least 40% to total weight is used. Furthermore,if the lubricant (perfluoropolyether) containing components having amolecular weight of at least 1000 and smaller than 4000 by at least 40%to total weight is used, the lubricant can be supplied stably to thesurface of the magnetic disk by heat and air flow, and not only thereduction of decrease of the lubricant film thickness, but also superiorsliding durability can be ensured.

[0070] (Embodiment 2)

[0071] In accordance with the embodiment 1, a supplying source oflubricant was provided on the suspension 15. In the embodiment 2, thelubricant was impregnated into a filter 8 and the filter was placed inthe magnetic disk drive as a supplying source of the lubricant. Thefilter 8 used was shaped a sheet of 10 mm long×10 mm wide×2 mm thick. Anexample of location of the filter placement is shown in FIG. 1.

[0072] Each of perfluoropolyether of No. 1 to No. 5 was dissolved into afluorine group solvent (HFE7100) by 40 wt %, the solution 20 μ-liter wasdropped into the filter 8 using a micropipette, and a random seek testwas performed under the same condition as the embodiment 1. The testresult is shown in FIG. 5. A case when perfluoropolyether was not usedis indicated as the comparative example 1.

[0073] In comparison with the comparative example 1, the case, when thefilter 8 impregnated with perfluoropolyether was provided, indicatedsmaller decrease of the lubricant film thickness, and superior slidingdurability by supplying the lubricant. As same as the result of theembodiment 1, the lubricant film thickness is almost constant value ifthe molecular weight is smaller than 4000. Accordingly, decrease of thelubricant film thickness at the surface of the magnetic disk 4 can bereduced significantly by using perfluoropolyether containing componentshaving a molecular weight smaller than 4000 by at least 40% to totalweight because the lubricant is supplied from the filter 8 by heat andair flow.

[0074] (Embodiment 3)

[0075] In accordance with the embodiment 3, the filter 8, which wasimpregnated with each of perfluoropolyether of No. 6 to No. 11, wasprovided into the testing apparatus 1, and how much the lubricant couldbe supplied to the surface of the magnetic disk was studied. The sampleswere obtained by molecular weight fractionation of perfluoropolyetherhaving the structural formula 1 for samples 6-8, the structural formula2 for sample 9, the structural formula 3 for sample 10, the structuralformula 5 for sample 11, and the structural formula 4 for sample 16. Asolution was prepared by dissolving perfluoropolyether of samples 6-16into a fluorine group solvent (HFE7100) by 40 wt %, and the solution 20μ-liter was impregnated into the filter 8.

[0076] Sample No. 6: Molecular weight 2000

[0077] Sample No. 7: Molecular weight 4000

[0078] Sample No. 8: Molecular weight 6000

[0079] Sample No. 9: Molecular weight 2000

[0080] Sample No. 10: Molecular weight 2000

[0081] Sample No. 11: Molecular weight 2000

[0082] Sample No. 16: Molecular weight 2000

[0083] The magnetic disk 4 (no lubricant) which is not applied with thelubricant is rotated for 24 hours, and then, thickness of the lubricantfilm on the magnetic disk is measured. The number of rotation is 5400rpm. The testing apparatus is not provided with the magnetic head slider2 nor the arm portion 3. During the rotation, inside the testingapparatus 1 was heated to 65° C.

[0084] The result is indicated in FIG. 6. In the evaluation of theembodiment 3, the lubricant's thickness of the samples 6, 7, 9, 10, 11,and 16 after 24 hours rotation are at least 0.3 nm. On the contrary, thelubricant's thickness of the samples 8 is smaller than 0.15 nm, and itis revealed that the lubricant supply is significantly small.

[0085] When the lubricant is not supplied from outside the disk surface(comparative example 1), decrease of the lubricant film thickness is 0.3nm per 24 hours. Then, if any one of the lubricants of samples 6, 7, 9,10, 11, and 16 is impregnated in the filter and used as the lubricantsupply source, the lubricant can be supplied stably to the surface ofthe disk by heat and air flow.

[0086] (Embodiment 4)

[0087] A schematic plan view and a schematic side view of the magneticdisk drive 14 are shown in FIG. 7. The magnetic disk drive 14 comprisesa magnetic disk 4 of 63.5 mm (2.5 inches) in diameter, housing 10,spindle motor 9, actuator 12, magnetic head slider 2, suspension 15, andcontrol circuit 13. On the surface of the magnetic disk 4, a lubricantmade of perfluoropolyether having a structure expressed by thestructural formula 1 and a number average molecular weight 3000 wasapplied with film thickness of 2 nm. The magnetic disk drive has aLoad/Unload mechanism. The magnetic disk drive 14 is provided with twomagnetic disks 4, and the volume of inside the device is 30.0 m-liter.Each of solutions which was prepared by dissolving each of the lubricantsample 6 (molecular weight 2000) and the lubricant having the structuralformula 6 (molecular weight 4000) into a fluorine group solvent(HFE7100) by 40 wt % was impregnated into the filter 8 by 1.25 μ-liters.

[0088] The sample, in which the lubricant expressed by the structuralformula 6 is impregnated into the filter, is designated as thecomparative example 2. The magnetic disk drive 14 having a radius in therange of 16 mm to 28 mm of the magnetic disk 4 was moved to random seek(a random seek test) under an environment of 65° C. for 1000 hours. Acase when the lubricant was not supplied was tested in the same way asthe comparative example 3. The load of the magnetic head slider 2 is 25mN, and rotation number of the magnetic disk 4 is 5400 rpm.

[0089]FIG. 8 indicates variation in film thickness versus deviceoperation time. The decreased in film thickness after 1000 hoursoperation is approximately 0.18 nm for the sample No. 6, andapproximately 0.37 nm for the comparative example 2. In case of thecomparative example 3 wherein the lubricant was not supplied, thedecrease in film thickness after 1000 hours operation was approximately1.2 nm. The decrease of the film thickness in cases of the sample 6 andthe comparative example 2 are reduced significantly by supply of thelubricant. This is because the effect of controlling the molecularweight as explained previously. The result having the same tendency wasobtained in case of providing three magnetic disks.

[0090] Next, photographs of the levitated plane of the magnetic headslider 2 after 1000 hours of random seek test were taken. The result isindicated in FIG. 9.

[0091] It can be clearly observed that smears are adhered significantlyon the levitated planes of the comparative examples 2 and 3 (nolubricant), but the smears are scarcely adhered in case of the sample 6.That means, the comparative example 3 has an advantage to supplylubricant (reduction of the film thickness decrease), but it hasscarcely the effect to prevent adhesion of smears onto the levitatedplane. Difference in structure of the sample 6 from the comparativeexample 2 is the presence of polar groups near the terminal endpositions of the molecule. It can be understood that the molecule havingthe polar groups reacts significantly with the levitated plane, andaccordingly, a stronger effect to prevent adhesion of smears thannon-polar lubricants such as the comparative example 3 is realized.

[0092] As explained above, supply of the lubricant having polar organicgroups in its molecule such as the sample 6 makes it possible to preventthe levitated plane of the magnetic head slider from adhering thesmears.

[0093] (Embodiment 5)

[0094] In the embodiment 5, the lubricant having the structure expressedby the structural formula 7 was applied onto the surface of the magneticdisk 4 with the film thickness of 2 nm.

[0095] Each of the lubricant (perfluoropolyether) of sample 6, 7, and 8was dropped by 1.0 μ-liter onto the plane, which faces to the magneticdisk 4, of the suspension supporting the magnetic head slider 2 at aspot 10 mm away from the magnetic head slider 2.

[0096] The magnetic head slider 2 was provided to the magnetic diskdrive 14 described previously in the embodiment 4, and was moved torandom seek (a random seek test) under the same condition as theembodiment 4 for 1000 hours. Then, variation in film thickness versusdevice operation time was measured. Furthermore, smears which adheredonto the sliding plane of the magnetic head slider 2 after the measurewas finished (after 1000 hours) were observed by optical microscope.

[0097]FIG. 10 indicates variation in lubricant film thickness versusdevice operation time. The comparative example 4 is the case when thesame test as the embodiment 5 is performed without dropping thelubricant onto the suspension (no supply of the lubricant) using thesame magnetic disk drive 14 as the embodiment 5. Furthermore, a casewhen the lubricant having the same molecular structure as the embodiment5, but its molecular weight is 850, is dropped onto the suspension istaken as the comparative example 5. In accordance with the comparativeexample 4, decrease of the film thickness after 1000 hours wasapproximately 1.1 nm. With the comparative example 5, decrease of thefilm thickness after 1000 hours was approximately 0.9 nm. This fact inaccordance with the test using the magnetic disk drive so far can beunderstood that the molecular weight of the lubricant in the comparativeexample 5 is smaller than 4000, and even if it may have the effect toreduce decrease of film thickness, the lubricant which scraped off bythe magnetic head slider 2 is larger than the amount of the lubricantsupplied to the surface of the disk, because of low sliding durability.In accordance with the sample 8, although the decrease of lubricant filmthickness after 1000 hours is smaller than the comparative example 4,the decreased amount of the lubricant film thickness is more than twotimes in comparison with the samples No. 6 and 7, and the effect ofsupplying the lubricant is small. On the contrary, the decrease of thelubricant film thickness of the samples No. 6 and 7 after 1000 hours issmaller than 0.25 nm, and it can be said that the effect with the supplyof the lubricant is significant and reliability as the magnetic diskdrive is superior. In accordance with the comparative examples 4 and 5,smears were adhered onto the sliding plane of the magnetic head slider2. On the contrary, no smears adhesion was observed on the slidingplanes of the magnetic head slider 2 of the samples No. 6 and 7.

[0098] In accordance with the results explained above, if the lubricant(perfluoropolyether) has a molecular weight larger than 1000 andcontains a component having a molecular weight smaller than 4000 by atleast 40 wt %, the lubricant can be supplied stably, and the magneticdisk drive having a preferable sliding durability and a superiorreliability to maintain a precise operability can be obtained.

[0099] (Embodiment 6)

[0100] In accordance with the embodiment 6, each of perfluoropolyetherof samples NO. 6 to 8 and the comparative example 2 was dropped onto thesuspension 15; a random seek test was performed in a manner as same asthe embodiment 3; variation in lubricant film thickness versus deviceoperation time was measured; and smears on the levitated plane of themagnetic head slider 2 after 1000 hours operation were observed withoptical microscope.

[0101] The magnetic disk drive as same as the embodiment 4 shown in FIG.7 was used. On the surface of the magnetic disk 4, a lubricant made ofperfluoropolyether having a structure expressed by the structuralformula 1 and a number average molecular weight 3000 was applied withfilm thickness of 2 nm. As a lubricant supply source other than thesurface of the magnetic disk, each of perfluoropolyether of the samplesNo. 6 to 8 and the comparative example 2 used in the embodiment 3 wasdropped by 1.0 μ-liter onto the suspension 15 plane facing to themagnetic disk 4 at a spot 10 mm away from the magnetic head slider 2.The case when perfluoropolyether of the comparative example 2 wasdropped was designated as the comparative example 6.

[0102]FIG. 11 indicates variation in lubricant film thickness versusdevice operation time. In case of the comparative example 3 wherein thelubricant was not supplied, the decrease in film thickness after 1000hours operation was approximately 0.8 nm. In accordance with the sample8, although the decrease of lubricant film thickness after 1000 hours issmaller than the comparative example 3, the decreased amount of thelubricant film thickness is more than two times in comparison with thesamples No. 6 and 7, and the effect of supplying the lubricant is small.On the contrary, the decrease of the lubricant film thickness of thesamples No. 6 and 7 after 1000 hours is smaller than 0.3 nm, and it canbe said that the effect with the supply of the lubricant is significantand reliability as the magnetic disk drive is superior.

[0103] In cases of the comparative examples of 3 and 6, smears wereadhered onto the levitated plane of the magnetic head slider 2, but suchadhesion of smears onto the levitated plan of the magnetic head slider 2was not observed in cases of the samples 6, 7, and 8.

[0104] In accordance with the results explained above, ifperfluoropolyether containing a component having a molecular weightsmaller than 4000, desirably larger than 1000 and smaller than 4000, byat least 40 wt % is used as a lubricant, decrease of the lubricant filmthickness at the surface of the magnetic disk 4 can be reducedsignificantly, because the lubricant can be supplied from the filter 8by heat and air flow.

[0105] Furthermore, if the lubricant (perfluoropolyether) having polargroups in its molecule is supplied, adhesion of smears onto thelevitated plane of the magnetic head slider 2 can be prevented, and themagnetic disk drive having a superior reliability can be obtained.

[0106] (Embodiment 7)

[0107] The lubricant sample No. 6 was dropped respectively by 1.0μ-liter onto the suspension 15 planes facing to the magnetic disk 4 ateach of spots 8 mm (sample 12), 15 mm (sample 13), and 20 mm (sample 14)away from the head element of the magnetic head slider 2. These magnetichead sliders 2 were provided to the magnetic disk drive 14 and testswere performed under the same condition as the embodiment 4.

[0108]FIG. 12 indicates variation in lubricant film thickness versusdevice operation time. In case of the comparative example 7, wherein thelubricant sample No. 6 is dropped at the spot 30 mm away from the headelement of the magnetic head slider 2, the decrease of the lubricantfilm is significant, and the lubricant is not supplied sufficiently. Onthe contrary, the decrease of the lubricant film is small in theembodiment 7. In case of the comparative example 8, wherein thelubricant sample No. 6 is dropped at the spot 3.0 mm away from the headelement of the magnetic head slider 2, the decrease of the lubricantfilm is scarcely observed. However, in the result of observation on thesliding plane of the magnetic head slider 2 after 1000 hours testoperation, adhesion of smears onto the sliding plane of the magnetichead slider 2 at the head element side was observed. On the contrary, incases of samples No. 12, 13, and 14, the adhesion of smears was scarce,and particularly, in cases of No. 12 and 13, the adhesion of strains wasnot observed at all. The adhesion of smears onto the sliding planeobserved in the comparative example 8 is because the spot whereon thelubricant is dropped is too close to the head element and the lubricantis oozed to the head element portion. In case of the comparative example7, wherein the lubricant No. 6 is dropped at the spot 30 mm away fromthe head element, the reason is assumed that the spot whereon thelubricant is dropped is too far from the element portion and a force ofthe air flow to supply the lubricant sufficiently is weak.

[0109] In accordance with the result explained above, the spot on thesurface of the suspension, whereon the lubricant is dropped, ispreferably in the range from 5.0 mm to 25 mm away from the head element.

[0110] (Embodiment 8)

[0111] A schematic plan view and a schematic side view of the magneticdisk drive 17 used in the embodiment 8 are shown in FIG. 13. Themagnetic disk drive 17 comprises a magnetic disk 18 of 76.2 mm (3.0inches) in diameter, housing 10, spindle motor 9, actuator 12, magnetichead slider 2, and control circuit 13. The magnetic disk drive 17 isprovided with a Load/Unload mechanism as same as the magnetic disk drive14. The magnetic disk drive 17 is provided with five magnetic disk 18,and inner volume of the device is 120 m-liter. On the surface of themagnetic disk 18, a lubricant film made of perfluoropolyether (numberaverage molecular weight 6000) having a structure expressed by thestructural formula 1 was formed with film thickness of 2 nm. Each ofsolutions which was prepared by dissolving each of the lubricant sampleNo. 6 and the lubricant having the structure expressed by the structuralformula 6 (molecular weight 4000) into a fluorine group solvent(HFE7100) by 40 wt % was impregnated into the filter 8 by 2.5 μ-liters(contains perfluoropolyether 1.0 μ-liters).

[0112] The sample, in which the lubricant expressed by the structuralformula 6 is impregnated into the filter, is designated as thecomparative example 9. These filters 8 were provided to the magneticdisk drive 17, and a random seek test were performed with disk rotationof 10000 rpm for 1000 hours. A case when the lubricant was not suppliedwas tested in the same way as the comparative example 10.

[0113]FIG. 14 indicates variation in lubricant film thickness versusdevice operation time. The decrease of the film thickness after 1000hours were approximately 0.22 nm for the sample No. 6, and approximately0.46 nm for the comparative example 9. On the contrary, in case of thecomparative example 10 wherein the lubricant was not supplied, thedecrease in film thickness after 1000 hours operation was approximately1.35 nm. The decrease of the film thickness in cases of the sample 6 andthe comparative example 9 are reduced significantly by supply of thelubricant. In the result of observation on the sliding plane of themagnetic head slider 2 after 1000 hours test operation, adhesion ofsmears onto the sliding plane of the magnetic head slider 2 was observedin cases of the comparative examples 9 and 10 (no supply of thelubricant) as same as the result shown in FIG. 9. On the contrary, incase of sample No. 6, the adhesion of smears was not observed at all.

[0114] In accordance with the result explained above, the reducingeffect on decrease of lubricant film thickness with the magnetic diskdrive corresponding to 3.0 inches disk can be realized by supplying thelubricant (perfluoropolyether). Furthermore, if the lubricant(perfluoropolyether) having polar groups in its molecule such as thesample No. 6 is supplied, adhesion of smears onto the levitated plane ofthe magnetic head slider 2 can be prevented, and the magnetic disk drivehaving a superior reliability can be obtained.

[0115] (Embodiment 9)

[0116] In accordance with the embodiment 9, variation in lubricant filmthickness versus device operation time was measured in cases when theamount of sample No. 6 (perfluoropolyether) dropping into the filter 8was changed. And smears adhered onto the levitated plane of the magnetichead slider 2 after 1000 hours operation were compared.

[0117] The apparatus used in the test was the same apparatus shown inFIG. 7 as the embodiment 4, and random seek tests were performed.

[0118] On the surface of the magnetic disk 4, a lubricant made ofperfluoropolyether (number average molecular weight 3000) having astructure expressed by the structural formula 1 was applied to form filmthickness of 2 nm. The amount of perfluoropolyether in the sample No. 6dropped into the filter 8 is as follows:

[0119] 0.1 μ-liter (containing perfluoropolyether 0.04 μ-liter)

[0120] 0.25 μ-liter (containing perfluoropolyether 0.1 μ-liter)

[0121] 0.375 μ-liter (containing perfluoropolyether 0.15 μ-liter)

[0122] 0.7 μ-liter (containing perfluoropolyether 0.28 μ-liter)

[0123] 1.25 μ-liter (containing perfluoropolyether 0.5 μ-liter)

[0124] 2.5 μ-liter (containing perfluoropolyether 1.0 μ-liter)

[0125]FIG. 15 indicates variation in lubricant film thickness versusdevice operation time. In case of the comparative example 3 wherein thelubricant was not supplied, the film thickness was decreased toapproximately 0.7 nm after 1000 hours operation. On the contrary, ifperfluoropolyether is contained at least 0.15 μ-liter, the decrease ofthe film thickness can be reduced. Furthermore, if perfluoropolyether iscontained at least 0.5 μ-liter, the decrease of the film thickness canbe reduced to smaller than 0.3 nm, that is, the decrease of the filmthickness can be reduced significantly. It is useful to adjust theamount of the lubricant impregnated into the filter depending on theinner volume of the device, and the number of the magnetic disksprovided in the device. In this case, it is also useful to consider theair flow depending on the structure of the device, and others.

[0126] A result of observation on the adhesion of smears onto thelevitated plane of the magnetic head slider 2 is shown in FIG. 16.

[0127] As shown in FIG. 9 previously, a large amount of smears wasadhered onto the levitated plane of the magnetic head slider 2 of thecomparative example 3 (no supply of the lubricant). In the casecontaining perfluoropolyether by 0.1 μ-liter, slight adhesion of smearsonto the levitated plane of the magnetic head slider 2 was confirmed,even though the amount of the smears is less than the case of thecomparative example 3 (no supply of the lubricant). On the contrary, noadhesion of smears were observed with the cases containingperfluoropolyether by 0.15 μ-liter and 0.5 μ-liter.

[0128] In accordance with the result explained above, although there maybe some fluctuation in number on account of influence by small gas ordust generated from various members in the device, if the amount ofperfluoropolyether of the sample 6, which is dropped into the filter 8,is equal to or more than 0.15 μ-liter, adhesion of smears onto thelevitated plane of the magnetic head slider 2 can be prevented, andfurthermore, if more than 0.5 μ-liter, an advantage to reduce thedecrease of the lubricant film thickness significantly can be obtained.

[0129] (Embodiment 10)

[0130] In accordance with the embodiment 10, an effect of supplyinglubricant to the operation system of the magnetic disk drive wasverified.

[0131] In the embodiment 10, a magnetic disk prepared by forming a seedlayer made of NiP film and Cr film, a magnetic layer made of CoCrTaPt,and a carbon overcoat sequentially onto surface of an aluminum substratewas used. Bump shaped protrusion was formed on the surface of the NiPfilm at a radius position in the range of 10 mm to 20 mm by laser.Accordingly, the bump shaped protrusion was also formed in a belt shape(laser zone) on the surface of the carbon overcoat at the same positionas the NiP film. Normally, the magnetic disk of this type is used forCSS (Contact Start Stop) system magnetic disk drive. On the surface ofthe carbon overcoat, a lubricant film made of perfluoropolyether(molecular weight 3000) having the structure expressed by the structuralformula 1 was formed by 2 nm thick.

[0132] The magnetic disk explained above was provided to the testapparatus shown in FIG. 1, and random seek test was performed as same asthe embodiment 2 for 120 hours. The seek was performed on a flat planeother than the laser zone. A solution prepared by dissolvingperfluoropolyether of sample 2 into a fluorine group solvent (HFE7100)by 40 wt % was dropped by 20 μ-liter into the filter 8 with amicro-pipette. After random seek test for 120 hours, rotation of themagnetic disk was stopped. Simultaneously, the magnetic head slider 2was saved onto the laser zone, and left it under a contacting conditionfor 24 hours. After 24 hours left, the magnetic disk was rotated again,and a stiction generated at the re-start of rotation and the lubricantfilm thickness on the surface of the magnetic disk after 120 hours' seekwere measured.

[0133] In accordance with the measurement of the lubricant filmthickness, the decrease of the film thickness from the initial filmthickness was approximately 0.6 nm, and almost same result with thesample No. 2 of the embodiment 2 was obtained. Then, it was revealedthat the decrease of the lubricant film thickness can be reducedsignificantly by supplying the lubricant. However, the stiction becamesignificantly high value such as 7.8 gf. That is, if lubricant issupplied in the CSS system, an adsorption between the magnetic disk andthe magnetic head slider is readily generated. Therefore, in order toreduce the decrease of the lubricant film thickness by supplying thelubricant with the CSS system, a countermeasure for preventing theadsorption such as forming protrusion on the levitated plane of themagnetic head slider, and the like becomes necessary. On the contrary,in case of the load/unload system, wherein the magnetic head slider isnecessarily saved to outside from the outer peripheral plane of themagnetic disk whenever rotation of the magnetic disk is stopped, it isnot necessary to consider the adsorption between the magnetic disk andthe magnetic head slider, and it can be said advantageous in view ofsupplying the lubricant.

[0134] In accordance with each of the embodiments explained above, thefilter 8 impregnated with the lubricant was used as the lubricant supplysource. However, the lubricant can be impregnated into any members whichcan hold the lubricant without causing dropping and the lubricant isreadily moved by temperature and air flow in the magnetic disk drive.For instance, gas adsorption filter, wick material, unwoven cloth,paper, and the like are usable. The same advantages can be obtained byadjusting the amount of the lubricant to be applied to the suspension orto be impregnated corresponding to the volume of the device. Forinstance, the present invention can be applied to the small sizemagnetic disk drives provided with small size magnetic disk such as themagnetic disks of 45.72 mm(1.8 inches ) in diameter, 33.02 mm (1.3inches), 25.4 mm (1 inch), and others.

[0135] In accordance with the present invention, the magnetic disk drivehaving a small decrease in lubricant film thickness on the surface ofthe magnetic disk and a superior sliding reliability between themagnetic head and the magnetic disk surface can be obtained.

What is claimed is;
 1. A magnetic disk drive comprising: a magneticdisk, a spindle motor for rotating said magnetic disk, a magnetic headslider for recording or reproducing data onto or from said magneticdisk, and a housing; further comprises: a control circuit system forcontrolling said head slider so that said head slider is positioned onthe magnetic disk plane when said magnetic disk is rotating, and saidhead slider is saved to outside the magnetic disk plane when rotation ofsaid magnetic disk is stopped; and a lubricant supply means forsupplying the lubricant to the surface of said magnetic disk; whereinsaid lubricant supply means contains at least one of perfluoropolyetherhaving a structure expressed by one of structural formulas 1 to 5 as alubricant, and said lubricant contains said perfluoropolyether having amolecular weight smaller than
 4000.


2. A magnetic disk drive comprising: a magnetic disk, a spindle motorfor rotating said magnetic disk, a magnetic head slider for recording orreproducing data onto or from said magnetic disk, and a housing; furthercomprises: a control circuit system for controlling said head slider sothat said head slider is positioned on the magnetic disk plane when saidmagnetic disk is rotating, and said head slider is saved to outside themagnetic disk plane when rotation of said magnetic disk is stopped; anda lubricant supply means for supplying the lubricant to the surface ofsaid magnetic disk; wherein said lubricant supply means contains atleast one of perfluoropolyether having a structure expressed by one ofstructural formulas 1 to 5 as a lubricant, and said lubricant containssaid perfluoropolyether having a molecular weight smaller than 4000 byat least 40%.


3. A magnetic disk drive comprising: a magnetic disk, a spindle motorfor rotating said magnetic disk, a magnetic head slider for recording orreproducing data onto or from said magnetic disk, and a housing; furthercomprises: a control circuit system for controlling said head slider sothat said head slider is positioned on the magnetic disk plane when saidmagnetic disk is rotating, and said head slider is saved to outside themagnetic disk plane when rotation of said magnetic disk is stopped; anda lubricant supply means for supplying the lubricant to the surface ofsaid magnetic disk; wherein said lubricant supply means contains atleast one of perfluoropolyether having a structure expressed by one ofstructural formulas 1 to 5 as a lubricant, and said lubricant containssaid perfluoropolyether having a molecular weight of at least 1000 andsmaller than 4000 by at least 40%.


4. A magnetic disk drive as claimed in claim 1, wherein said lubricantcontains perfluoropolyether having a structure expressed by thestructural formula 1, and said lubricant supply means is any of asuspension applied with said lubricant and an arm applied with saidlubricant.
 5. A magnetic disk drive as claimed in claim 1, wherein saidlubricant supply means includes a lubricant holding means for holdingsaid lubricant.
 6. A magnetic disk drive as claimed in claim 5, whereinsaid lubricant holding means is a filter impregnated with saidperfluoropolyether by at least 0.5 μ-liter.
 7. A magnetic disk drive asclaimed in claim 5, wherein said lubricant holding means is a filterimpregnated with any one of perfluoropolyether having a structureexpressed by any one of the structural formulas 1 to 5 by at least 0.15μ-liter, characterized in having scarce smears on the levitated plane ofsaid magnetic head slider.
 8. A magnetic disk drive as claimed in claim1, wherein lubricant film on said magnetic disk contains at least anyone of perfluoropolyether having a structure expressed by any one of thestructural formulas 1 to 4.